RBL refer to Real Time Blacklist or Sometime Real Time Block list by some peoples. Real time blacklists are  internet repositories which helps to protect web companies by monitoring email domains & IP addresses to find and control email spam sources.

How does real time blacklist works?

RBL uses spam trap or honey trap email accounts to identify spam sources for domains and IP addresses. Whenever any email server hits this traps, RBL repositories extract that email for analysis and then make decision about spam sources are true or false. There are more than 250 RBLs are working over the internet, however not more than 50 are working well and considered by many email and web hosting companies.

What is spam traps or honey traps?

Legitimate mailers or email marketing companies always consider and allow only double or confirm opt-in emails to send marketing emails. On the other hand spammers or high volume senders either uses email contact scrapping tool or use single opt-in method to build email list faster. It is the loop hole where spam traps get entered into their list and whenever they email to that contacts, their source has caught by RBL engine.

Some most popular real time blacklist service providers

Almost all real time blacklist providers are non-profit organizations and supported by big internet companies.

Spamhaus.org

Spamhaus is top among all RBL providers. Spamhaus work for both domain and IP addresses. It punishes hard to any spam source and also ISPs.  Spamhaus is considered widely by ISPs and internet companies.

BarrcudaCentral.org

Barracudacentral.org is operated by Barracuda network. Barracuda network is involved to produce most trusted firewalls & spam filter for internet users and companies. It is working for IP and required manual de-listing.

Spamcop.net

It is a well know spam filter in internet world. spamcop listed spam activity against only spamcop users. It works for IP only and required manual de-listing.